Method of changing resistance in a circuit and apparatus therefor.



E. W EINTRAUB.

METHOD OF CHANGING RESISTANCE IN A CIRGUIT AND APPARATUS THEREFOR. APPLICATION FILED APR. I3, I9I6.

1,24%,150. Patented Oct. 1917.

E .11 a a I C r v f7 -42.. W/E/\/7'DR: F 765 ft juigid Q; a {Hf m 4 1 m I rmp UNITED satires EZEGHIEL WEINTRAUIB, or BOSTON, MASSACHUSETTS, ASSIGNOIR. T0 sufeivianmn SIGNAL COMPANY, or PORTLAND,

MAINE,.A CORPORATION OF MAINE.

METHOD OF CHANGING RESISTANCE IN A CIRCUIT AND APPARATUS THEREFOR.

Application filed April 13, 1916. Serial No. 90,861.

To all whom it may concern Be it known that I, EZEGHIEL VVEINTRAUB, of Boston, in the county of Suffolk and State of Massachusetts, a citizen of the United States, have invented a new and useful Improvement in Methods of Changing Resistance in a Circuit and Apparatus Therefor, of which the following is a specification.

The present invention is a newtype of microphone capable of varying a much larger current than has been possible in the past, and of accomplishing this variation in better conformity to the sound variations that are to be reproduced.

The important applications of this invention are in long'distanci telephony, wireless telephony, submarine. signaling, and in all other cases where variation by means of voice or sound in general of larger amounts of energy than heretofore possible is desired.

In a microphone the sound waves produced by the voice impinge upon a diaphragm and force it to move backward and forward in conformity with the impressed sound waves. The diaphragm actuates one of the electrodes of an imperfect contact. The imperfect contact thus arranged is conneeted in an electrical circuit and the movements of the diaphragm and the consequent movement of its associated electrode produce changes in the resistance of/ the circuit betweenthis electrode and another or other associated electrodes. The object 'in the design of a microphone is to produce changes in the resistance of an electrical circuit similar to the changes in the compressional air waves of the voice and to make such changes in resistance take place through as wide a range as possible without making the resistance infinite, that is to say, without breaking the circuit at the point of contact.

. In the past it has been usual to employ carbon for one or both of the electrodes of the imperfect contacts of microphones. Moreover, to prevent the circuit being broken at the electrodes by an excessive movement of the associated receiving diaphragm, it has been usuahof late-years to intcrpose' finely divided particles of carbon between the front and back electrodes. The

I Specification of Letters Patent.

Patented Oct. 23, 1917.

use of, finely divided or granular carbon has a still further advantage in that it affords a large number of paths for the current passing between the front and the back electrodes. For a given current passing through the circuit this subdivision of the current in the microphone prevents such an excess of current passing. at any one point as will produce'arcing at that point, with a consequent destruction of the surfaces of the electrodes and the production of foreign disturbing noises known as burning or hissing.

In designing a microphone, therefore, the object sought must be to so form the electrodes and current-varying medium that the current will be varied-through the widest possible range without burning and without the circuit ever becoming broken;

There is still another point to. be considered. The heat at the small points of contact becomes considerableand the material used for the electrodes must be such that their temperature is raised. 'This is explained in modern theory by assuming emission of negatively charged corpuscles, socalled electrons. The hotter the electrodes the larger the number of these electrons, the "greater thecurrent that can be carried, and thegreater also the distance to which the electrodes can be separated wi hout an actual break of circuit.

When carbon or similar material is used it is necessary to avoid the presence of ,oxygen or oxidizing gases as these would cause rapid combustion at the elevated temperature used. The absence of oxygen is also instrumental in preventing burning and hissing. I have discovered that even traces of oxygen, water vapor, or other oxient invention in an inert medium, free from such active gases. As such an inert medium I prefer to use either a vacuum or one of the rare gases especially argon.

At the temperature used in the present invention it becomes possible to utilize other substances than carbon, substances which hitherto have never been successfully employed as the current-varying media of microphones. Thus it is well known that certain metallic oxids at high temperatures decrease inresistance and emit electrons at a rate exceeding that characteristic of metals or carbon, thereby making possible a larger range of electrode movement without welding or breaking circuit.

Oxide have never before been found comparable with carbon as current-varying media. The reason for this has been due partly to the high resistance usually inherent in such substances when cold but more especially to the fact that when cold lectrons can not pass readily from the mass and as a consequence the range of movement oi? the electrode without interruption to the circuit is extremely small. When heated to a high temperature both of these defects are clinics natcd.

In view of the above I have devised apparatus shown in the drawings in its pre ferred form, but not necessarily limited to the form there shown. In these drawings- Figure l is a longitudinal section of apparatus embodying; this invention;

Fig. 2 showing a modification thereof, and

Fig. 3 showing diagrammatically the electriccircuits, etc, which may be used in carrying out my invention.

Fig. 4c shows a further modification described below, the spiral being in perspective and the casing in section.

1 is the metal diaphragm such as is usual in microphones and which is actuated by compressional voice or other sound waves in the air. 2 is a rod attached to the diaphragm by a fastening means as at 6, and.

carrying the front electrode 4, which, how- I ever, may be integral with it. The rear electrode 5 is attached preferably to the rod 3 and maybe adjusted to and from the electrode 4.- by means of the adjusting screw 7 to which the rod 3 is attached.

Concentric with the rods 2 and 3 is a heater inclosing the electrodes 4: and 5. It

. lay be variously constructed, but as shown it is electrical and consists of a highly refractory tube 8 aboutwhich is wrapped a spiral of resistance wire 9 outside of which i is a layer of insulating material 10. Sun,

rounding the heater is a quartz tubell secured metal ends Hand 13 by which it is securely held in place, and the ext rior may be water-cooled, it desired. In the metal end 13 are insulating bushings lei, 16 and 1'? neeaieo V by means of the clamping ring 21, which may carry the ordinary telephone mouth piece 2:2. The oints in this device are all made gastight, "and the tubes 19 and 20 should be connected either to an air pump so that the chamber within the heater may be made a vacuum chamber, or else to a rcserroir of inert gas by which the chamber. may be iille'd..

in the modification shown in Fig. 2, the electrodes at and 5 are differently shaped and do not touch, but-the end of one of their is formed to containgranules of electrode material, for example, carbon, or for high resistance microphone metallic oxids, and the end oi? the other is constructed to hold these granules in place; the two forming a box or casing for the, granules which make contact between both rods.

in Fig. 3 there is shown the preferred arrangement of circuits in which the heater 2% is energized by the battery 25, or any other source of current. The current between the electrodes t and 5 is energized by the battery 27 for which the rods 2 and 3 serve as con ductors to the electrodes. Variations of this latter current are "caused by inicrophonic action at the electrodes l and 5 and are transformed by the transformer 26 to a secondary current 28.

Referring to Fig. 1, it is evident that if the rods 2 and 3 are made of such small section thatlittle heat vmay be conducted by them, the electrodes land 5 maybe heated to a temperature sulli'ciently high by means of the current passing between them, but under ordinary conditions the separate heater is desirable. Their length is immaterial so long as they furnish means of supporting the electrodes under the required conditions of heat. a

In Fig. 4 I have shown another form of my invention in which one of the electrodes 30 is formed as a spirala'nd heated to the high temperature required by an auxiliary current passing through it. In this view the diaphragm 1 has attached to it'a rod 31, perpendicular to the plane of the spiral, the end of which rod terminates in the center of the spiral 30. The rod is connected with abattery 32 and a receiver 33 by the wires 34, one of which is connected to the spiral 30. The heating-circuit comprises the wire 355, battery or other source of current 36 and the connection between 36 and the spiral 80. The whole is inclosed in an airtight casing sistmg in maintaining a at a high temperature.

power, one which is free from foreign disturbances, and is capable of varying currents never before used in telephone transmitters.

Other forms falling Within the scope ofmy invention will suggest themselves to those skilled in the art, my invention conone or-both' electrodes What I claim as my invention is:

1. That method of changing resistance in a microphonic circuit which consists in heating one or both of the electrodes of the microphone to a proach and retraction of said electrodes.

2. That method of changingresistance in a microphonic circuit which consists in heating one or both of the electrodes of the microphone in the a temperature above that of initial incandescence and causing theapproach and retraction of said electrodes.

3. A microphone and means for maintaining the microphonic contacts thereof at a temperature .above initial incandescence in an atmosphere freed from oxygen.

4. A microphone inclosed phere of one of the chemically inert gases temperature above that of rinitial incandescence and causing the ap presenceof an inert gas to I in an atmos and means for maintaining the microphonic contacts thereof initial incandescence.

5. A means for changing resistance in a -c1rcuitcomprising two electrodes of whichone or both are movable, agranular material between them, and means to maintain the whole at a temperature above initial incandescence.

6. A microphone comprising electrodes located in an exhausted space and maintained at a temperature above initial incandescence and means for maintaining said electrodesat such temperature.

microphone comprising two elec- 50 trodes one or both of which are movable and separated by material such as oxids, nitrids or the like, which become conductive at a temperature above initial incandescence, and

'means .for maintaining them at such temperature.

at a temperature above 8. That method of changing resistance in a'mlcrophonic circuit which consists in heating one or both of the electrodes of the microphone to a temperature at which ther mionic emission is effected and causing the approach and retraction of said electrodes,

9. A microphone inclosed'in an atmosphere of one of the chemically inert 'ases, and means for maintaining the microp contacts at a temperature at which ther- "mionic emission is efi'ective.

EzEoH'IEn WEINTRAUB,

onic 

